A monitoring system, which photographs a work floor, on which various work such as warehousing, sorting, and shipping are performed, by using a camera, and monitors the status of the work floor by using the images of the camera, is adopted in distribution centers, but there is a demand for a capability of checking the transport status of a package on the work floor in video of the camera, and when images are used with such an aim, unlike a case in which images are used with the aim of monitoring for crime prevention and disaster prevention, it is desirable that the privacy of people such as employees present on the work floor be protected.
In response to the demand to protect the privacy of such people, techniques for performing a masking process (a concealment process), which changes people regions in video photographed by a camera to a specific masking image, are known in the related art (refer to PTL 1 and PTL 2). In these techniques, a masking process is performed for image regions of moving bodies by detecting moving bodies by using a background differential system that extracts a foreground image through comparison with a background image.